A critically important number that sets the expansion rate of the Universe, the so-called Hubble constant, has been independently determined using NASA's Chandra X-ray Observatory. This new value matches recent measurements using other methods and extends their validity to greater distances and thus allows astronomers to probe earlier epochs in the evolution of the Universe. These images show six of the 38 galaxy clusters that scientists observed with Chandra.
[Runtime: 0:16](Credit: NASA/CXC/MSFC/M.Bonamente et al.)